1. Field of the Invention
Applicants"" invention relates to a device for measuring intrauterine pressure and fetal heart rate and method for same. More particularly, it relates to a device that employs a Foley-type urinary drainage catheter with a sensing member to measure pressure within the bladder or rectum and correlate the measured pressure to the pressure exerted within the patient""s uterus. Additionally, a fetal heart rate sensing member at or near the tip of the catheter is used to measure fetal heart rate from within the maternal bladder or rectum.
2. Background Information
Electronic fetal monitoring is a mainstay of fetal surveillance before and during labor. Much of the analysis focuses on the fetal cardiac responses to various intrinsic and extrinsic provocations, including contractions. Electronic fetal monitoring can predict the absence of asphyxia with greater accuracy than other conventional techniques. Electronic fetal monitoring can improve prenatal outcome by reducing the risk of intrapartum stillbirth and low Apgar scores. It also facilities the physician""s ability to diagnose potential abnormalities during labor and allows for early intervention, such as emergency cesarian sections.
Electronic fetal monitoring can employ several modalities. Two of the most common and helpful are measurements of the intrauterine pressure and fetal heart rate. By monitoring the patterns of the fetus"" heart rate in time with the intrauterine contractions, the physician can assess possible fetal distress.
Currently, uterine contractile events and fetal heart rate are monitored by external sensors or intrauterine devices. External monitors are safe and noninvasive, but are limited by their inability to assess intrauterine pressure intensity and are hampered by artifacts introduced through sensor placement and abdominal wall thickness. In contrast, internal monitoring provides the physician with more accurate monitoring but requires placement of a monitoring device within the uterus, and on many occasions, placement of a fetal scalp electrode. This type of device requires rupture of the amniotic sac for proper placement. Once the physician determines that internal electronic fetal heart monitoring is advisable, the physician must rupture the sac, irreversibly committing the fetus to delivery. Additionally, the placement and use of an intrauterine device carries risk of placental abruption, chorioamnionitis, fetal laceration, uterine laceration, umbilical cord laceration, and uterine perforation. If a fetal scalp electrode is used, the physician must insert the wire device into the scalp of the fetus which carries risk of fetal bradycardia as well as other risks of infection, bleeding, scarring, and injury.
Even without significant complications, the fetal scalp electrode and the intrauterine pressure catheter partially obstruct the cervical and vaginal canal after placement. The devices may, therefore, interfere with the delivery by their mere presence due to the health provider""s hands, instruments, and the baby passing through these same canals.
It would also be advantageous for healthcare providers to be able to monitor the quality of maternal uterine contractions. All muscular activity involves electrical signals that can be detected, including the maternal uterus when contracting during childbirth. An analysis of these signals can provide the healthcare provider with valuable insight regarding the strength, duration, intensity, and change over time of contractions.
Thus, there is a need for a method and device for monitoring intrauterine pressure and fetal heart rate that is more accurate than external devices but safer and less invasive than intrauterine device placement. Further, it is advantageous for the method to avoid placement of the device within the cervical or vaginal canals. Thus, the apparatus must be capable of providing the physician accurate information from a location other than the uterus, cervical canal or vaginal canal. Further, it is advantageous if the device were also capable of measuring the myoelectrical activity of the maternal uterus.
The present invention incorporates a modified Foley catheter that transmits desired data to transducers allowing monitoring of intrauterine pressure and fetal heart rate by healthcare providers on appropriate output devices. The method of the present invention employs an apparatus to indirectly measure intrauterine pressure and fetal heart rate from within the maternal bladder.
The present invention provides a novel apparatus that will permit the minimally invasive monitoring of a fetus for signs of distress before and during labor. Collected data will provide the physician with improved information to assist in the decision of whether to proceed with more invasive monitoring techniques or emergency procedures, including cesarean sections. Earlier monitoring and intervention may lead to a decrease in the rate of cerebral palsy due to hypoxic injuries sustained during delivery.
The present invention further provides:
a. a novel apparatus for accurately measuring intrauterine pressure, while alleviating the risks associated with conventional, intrauterine devices;
b. a novel apparatus for measuring fetal heart rate as it responds to stimuli, including uterine contractions;
c. a novel apparatus for measuring maternal, uterine myoelectrical signals;
d. a novel apparatus and method to allow the physician to monitor uterine contractions and fetal heart rate from within the maternal bladder without rupturing the amniotic sac and committing the fetus to deliveryxe2x80x94allowing the physician to more liberally order such monitoring, not only at the time of delivery, but throughout pregnancy;
e. a novel apparatus and method to allow said measuring with minimal or no obstruction of the cervical and vaginal canalsxe2x80x94allowing the physician to work without the interference of wires and/or catheters;
f. a novel method for accurately measuring intrauterine pressures and contractions, including frequency, intensity, and duration of the contractions from the maternal bladder;
g. a novel method for obtaining maternal uterine electromyographic data to better delineate the quality of uterine contractions; and
h. a novel method for accurately measuring fetal heart rate simultaneously with measuring uterine pressure and using the same apparatus.
In order to solve the difficulties presented in attempting to obtain these features, a modified Foley catheter and transducer apparatus has been developed which is designed for insertion in the bladder or rectum.
Specifically, the present invention provides for a method and device for indirect monitoring of intrauterine pressure by using direct pressure measurements within the maternal bladder. Simultaneously, the present invention is capable of measuring the heart rate of the intrauterine fetus. Pressure changes within the uterus have corresponding pressure changes in the maternal bladder. Thus, contractions occurring within the uterus are indirectly measurable within the bladder. The present invention employs a modified Foley-type catheter with an integral balloon near the insertion tip that may be filled with fluid. The catheter is inserted in the maternal bladder and the catheter balloon is filled with fluid, securing the insertion tip within the bladder. Urine within the bladder is drained through a drainage port and canal, allowing the tissue surrounding the bladder to collapse snugly against the balloon and insertion tip. In a first embodiment, the fluid filled balloon is in communication with a pressure transducer outside the patient""s body via a continuous fluid channel. Thus, as contractions and other pressure changes occur within the uterus and the intraabdominal cavity, they are correspondingly exerted upon the pressure sensing member which indirectly measures intrauterine pressure. If the present invention employs the balloon as the pressure sensing member, pressure exerted in a mechanical fashion on the balloon is transmitted through a communicating, fluid-filled channel to a pressure transducer. An alternative embodiment of the present invention employs an electronic pressure sensor to measure pressure, in which case the resultant electronic signal is communicated along electric leads from the sensing member to the connectors.
The modified Foley catheter has fluid conduits molded into the tube wall material to provide a passage to inflate a balloon near the insertion end for anchoring the catheter in the body. The filled balloon anchors the catheter within the bladder or rectum due to its larger diameter compared to the diameter of the urethra or rectum.
An electrode, or microphone may be inserted or embedded in the catheter near the insertion end to serve as a fetal heart rate sensor. Electrode type sensors are sensitive to the electrical signals produced as the result of muscular activity. Thus, contractions of the fetus"" heart produces an electrical signal that is measurable by the electrode type sensor. Alternatively, if an electrode is used, it will also serve to measure maternal, uterine myoelectrical signals. The choice by the healthcare provider to measure fetal heart rate or maternal, uterine myoelectrical signals is a matter of choosing the appropriate signal processing filter to isolate the desired signal. An electronic lead incorporated into the catheter and attached to the heart rate sensor would provide communication to connection end. Alternatively, a Doppler ultrasound probe may be inserted through the catheter utilizing the catheter as a sterile sheath. External transducers and output devices such as monitors or printers, may be connected to the connection end of the catheter and provide for monitoring by the healthcare provider.
The catheter is generally inserted through the urethra into the bladder of the patient, but can be inserted into the rectum as well. Inflation of the balloon anchors the insertion end of the catheter in the bladder and/or rectum. The catheter contains a drainage channel that is open at the insertion end and allows for complete drainage of the bladder.
Pressure changes within the bladder correlate with strong statistical significance to the changes in intrauterine pressures. During pregnancy, contractions and other intrauterine pressure changes are transmitted through the intraabdominal cavity and onto the pressure sensing member of the present invention. When the inflated balloon is being used as the pressure sensor, the fluid channel that allows for inflation of the balloon can be connected to a pressure transducer to measure the mechanical pressure changes on the balloon and convert the pressure changes into numerical measurements that are interpretable by the physician. These pressure measurements correlate with the frequency, strength and length of contractions during labor.
Alternatively, other pressure measuring members may be utilized, such as using a pressure transducer to measure pressure in place of the filled balloon and fluid filled channel. The transducer provides pressure measurements via electrical communication with appropriate output devices. Generally, if a pressure transducer is used, the balloon will be used solely for anchoring purposes. However, should it be desirable, the pressure transducer may be used in combination with the pressure sensing balloon, such that two (2) pressure readings are obtained. The pressure transducer may be located at or near the insertion end of the catheter, or within the balloon itself.
In order to monitor fetal heart sounds and/or rate, an electrode, Doppler ultrasound probe, or microphone apparatus may be implanted or inserted in the catheter wall or lumen at or near the insertion end of the catheter. This places the measuring device or electrode within the maternal bladder, in close proximity to the fetus lying within the uterus. The signal from the fetal heart sensing device may be digitally processed to augment fetal heart signals and/or heart sounds while diminishing or eliminating unwanted signals and sounds such as the maternal electrical signals and/or maternal heart sounds. Alternatively, the signal processing may focus upon maternal myoelectric uterine activity. These signals are then converted into measurable data that is meaningful to the healthcare provider.
The fetal heart monitoring member of the present invention can be configured in a number of ways consistent with the physical requirements of the invention. It may be reusable, and removably insertable in the catheter, or it may be built into the catheter and disposable. The sound sensor may be entirely within the catheter, exposed to catheter environment, or held within a balloon that can be filled with an acoustically enhancing medium.
The method of use of the present invention involves inserting the catheter insertion (distal) end through the mother""s urethra into her bladder. The balloon is then inflated, anchoring the insertion tip within the bladder. Generally, urine is then drained from the bladder through the catheter, leaving the balloon and sensors in close contact with the bladder walls. At the connection (proximal) end of the catheter, the fluid filled channel is connected at its outlet end to a pressure transducer. Alternatively, if an internal pressure transducer is being employed, then electronic leads connect the transducer to outside monitoring devices. The fetal heart sensor is likewise connected via electronic leads to outside monitoring devices. Each transducer is attached to a chosen output device, for example a monitor or printer, and the physician is able to monitor the condition of the fetus. Alternatively, the physician would employ the same basic method, however inserting the catheter into the patient""s rectum and securing the insertion (distal) end of the catheter at a desired position in the rectum or large intestine. It is possible that both the bladder and rectal methods may be used simultaneously.